This PR adds functionality to the evm t8n to calculate ethash difficulty. If the caller does not provide a currentDifficulty, but instead provides the parentTimestamp (well, semi-optional, will default to 0 if not given), and parentDifficulty, we can calculate it for him.
The caller can also provide a parentUncleHash. In most, but not all cases, the parent uncle hash also affects the formula. If no such hash is provided (or, if the empty all-zero hash is provided), it's assumed that there were no uncles.
This PR implements the EVM state transition tool, which is intended
to be the replacement for our retesteth client implementation.
Documentation is present in the cmd/evm/README.md file.
Co-authored-by: Felix Lange <fjl@twurst.com>
